We propose a cosmic-ray muon spin rotation radiography to investigate physical and chemical status of steels in large-scale architectures based on the experimental results obtained for Fe and concrete by using cosmic-ray and accelerator muons. Spin polarized positive muons contained in the cosmic rays were stopped in the Fe plates providing a characteristic spin rotation signal of decay positrons. Signals of decay electrons from negative muons stopped in Fe are separated from those of decay positrons, by nature of different lifetimes of negative muons in heavy elements. After subtraction of decay electrons, we have successfully extracted muon spin rotation with 47.2±0.7MHz in frequency and 8.7±4.6 μs-1 in relaxation rate. These values are consistent with those obtained by reference experiment by using intensive muons provided by an accelerator, verifying validity of analysis. This method is quite promising to investigate steels at near-surface (20 cm thick from the surface).